THE PARADOX OF NEGATIVE EXERCISE STRESS ECG POSITIVE THALLIUM SCINTIGRAM - ISCHEMIC ST-SEGMENT COUNTERPOISE AS THE UNDERLYING MECHANISM/

A 62-year-old woman with exertional angina underwent an exercise thall ium-201 stress test. She exercised for 4 minutes on the treadmill usin g a modified Bruce protocol, reaching 94% of her predicted maximal hea rt rate, and stopped because of chest pain and fatigue. No ST-segment depression was detected at peak exercise or in the recovery period. In contrast, the thallium-201 myocardial single-photon emission computed tomography images in the short-axis, vertical long-axis, and horizont al long-axis views revealed severe myocardial ischemia involving the a nterior, septal, posteroinferior, and posterolateral planes of the hea rt. Coronary arteriography showed severe stenosis of the left anterior descending and right coronary arteries. The information from the exer cise electrocardiogram (EGG), thallium-201 myocardial scintigraphy, an d a coronary angiogram suggested that the false negative ECG response was due to ischemic ST-segment counterpoise tie, cancelation of ischem ic ST-segment vectors, generated by equally extensive and severe ische mia involving myocardial planes opposite each other.